1. Field of the Invention
The present invention generally relates to electrochemical cells and more particularly to an improved method of charging vented alkaline electrolyte-containing electrochemical cells.
2. Prior Art
In certain electrochemical systems, particularly those having alkaline electrolytes, determination of the state of charge cannot be reliably ascertained except by discharging the cell. Obviously this is undesirable since in most circumstances a fully charged cell is wanted. If the battery or cell is charged without being able to determine when the full charge occurs, there is a danger of overcharge and impairment of the cell.
In the case of a closed cell, for example, employing nickel oxide and cadmium electrodes or the like, if the cell is charged at a relatively low rate, generation of oxygen at the nickel oxide electrode normally is matched by oxygen consumption at the cadmium electrode so that the oxygen gas pressure in the cell does not build up to a dangerous level. If a higher charge rate is used, however, dangerous oxygen build-up can occur and may result in an explosion. However, such a closed system can employ an auxiliary electrode to signify the pressure condition in the cell and thus dictate other interruption of the charging or a reduction in the charging rate whenever the gas pressure in the cell exceeds a predetermined level. Such safety procedure is not available when a vented or semi-sealed cell is used. Such cells employ mobile electrolyte and changes in the electrolyte level do not permit a reliable signal.
Accordingly, there is a substantial need for an improved method of detecting the charged condition of a vented electrochemical cell during the charging procedure and of preventing overcharging of the cell.